Spring vs coilovers stiffness confusion
 

Can some1 explain spring rates on springs vs coils? I no there is no way in hell if my eibach SPORTLINES are 3.8k up front that KW3 coils are almost twice as stiff at 6.1k

Its the damping curve that the springs are matched to. The stock shock dyno is what is used to develope lowering springs for stock shocks. Thats why you dont see 6k & 8k lowering springs for the stockers.

The damping is more aggressive and the shock travel is shorter on the KW's, thus requiring a firmer spring.

Stiff has kind of a harsh negative connotation to it, firm is a better description of a properly matched spring and damper combo.

Spring rates are spring rates, no voodoo involved. The K stands for kg/mm, meaning it takes 3.8kg or 6.1kg to compress the springs 1mm. Lbs/in is the same, just different units.

The V3's are also coming with softer springs now, IIRC it's more like 280F and 340R, which would be 5kg/mm and 6kg/mm. Either way, yes the V3's are significantly stiffer than sportlines.

Damper quality plays a HUGE part in how a car rides, with really high quality dampers you can run much higher spring rates and still ride decently well on the street.

Are dampening rates (for lack of a better term) ever listed?

The force on the car chassis when you hit a bump is the sum of the spring rate + the damping force.

Higher end dampers have more sophisticated valving which allows oil to flow very freely at high speed. The net result is a 6kg spring on a good damper puts less of a jolt on the cars chassis than a lower end one that struggles to let the oil flow at quickly.

You might see shock dynos posted, but generally not. It's the quality, not the damping rate, that lets a really stiff spring ride nicely.

You might be interested in reading this thread:
http://www.ft86club.com/forums/showthread.php?t=81062

- Andrew